On account of superconductor characteristics at temperatures of boiling nitrogen (77 K) and above, materials having one of two recently discovered compound structures show significant and potentially revolutionizing technological promise. Among representatives of the first such structures are compounds in the La-Ba-Cu-O and Y-Ba-Cu-O systems; representative of the second are bismuth-strontium calcium cuprates having representative composition Bi.sub.2.2 Sr.sub.2 Ca.sub.0.8 Cu.sub.2 O.sub.8+.delta., with .delta. in the vicinity of 0.2. In this respect see also, e.g., the paper by M. A. Subramanian et al., "A New High-Temperature Superconductor: Bi.sub.2 Sr.sub.3-x Ca.sub.x Cu.sub.2 O.sub.8+y ", Science, Vol. 239, pp. 1015-1017 (1988).
While many properties of these materials can be studied in sintered polycrystalline samples, it is desirable to provide single crystals of macroscopic dimensions, e.g., for the purpose of determining correlations between structural parameters and superconductor properties. Also, as contemplated superconductor applications include the use of thin, possibly patterned superconductor layers having significant current-carrying capability, and as such capability is likely to be highest in single-crystal material, there is strong interest in epitaxially deposited single-crystal layers, e.g., in switching and logic device technology.